Along with progress in recent IT (information technology), the number of devices making use of networks shows a vast increase. In this situation, in particular in view of usability, there are increasing demands for wireless networking technology. An RF front-end module used for radio communication has, beside a semiconductor chip, relatively large-sized components, such as SAW (surface acoustic wave) filter and dielectric filter used for RF filter (high frequency filter) and IF filter (intermediate frequency filter), incorporated therein, so that presence of these components is causative of inhibiting miniaturization and cost reduction of the RF front-end module. Therefore, efforts has been made on realizing miniaturization and cost reduction of the RF front-end module, by incorporating these filter functions into a semiconductor chip. More specifically, there is known a technique of using a MEMS (micro-electro-mechanical system) element, a sort of micro-machine, as a resonator.
A resonator employing the MEMS element (referred to as micro-resonator, hereinafter) is formed on a semiconductor chip using semiconductor processes, and has a beam structure allowing the device to function as a resonator. The micro-resonator has advantages in that the device needs only a small space to occupy, can realize a high Q value (ratio of energy/loss), and can be integrated with other semiconductor devices. Therefore, a proposal has been made on using it as a radio communication device, especially as a frequency filter (RF filter, IF filter) (see, for example, High-Q HF Microelectromechanical Filters, “IEEE Journal of Solid-state Circuits”, (U.S.A.), April 2000, Vol. 35, No. 4, p.512-526).
However, the micro-resonator disclosed in the above-described High-Q HF Microelectromechanical Filters has an extremely large Q value, and a specific bandwidth obtained in a case where the filter device is configured by mechanically connecting (coupling) beam electrodes of two micro-resonators with a rod-like elastic strip is only as small as 1% or below (0.23% according to the description in the document). In contrast to this, most of specific bandwidth required for the filter device is 2% or above, so that there has been a need of expanding the specific bandwidth in order to satisfy the demand.
The present invention was conceived in order to solve the above-described problems, and an object thereof resides in realizing expansion of the specific bandwidth of a filter device configured using micro-resonators.